The fossil fuels of today largely came from the aquatic single-celled photosynthesizers of yesterday: Nourished by sunlight and high levels of atmospheric carbon dioxide, these microalgae formed vast colonies on the surface of Earth’s ancient oceans, and when they died, they sank to the seafloor, building up in thick layers that gradually decomposed to form hydrocarbons like petroleum and natural gas.

Algae may have been the source of the oil we’re addicted to, but they could also help wean us off it by acting as a feedstock for biofuels. Most existing biofuel feedstocks, like those used to make ethanol or biodiesel, rely on the sugars, starches, or oils from the energy-intensive farming of food crops. Algae, by comparison, do not require land or clean water to grow. They flourish anywhere there is water, sunlight, and carbon dioxide, and can yield much more energy-per-acre than most other biofuel crops. In addition, algae can be engineered to secrete biofuels, which can be siphoned off without damaging the organisms themselves.

In a watershed July 14 announcement, Exxon Mobil, the largest non-state-owned oil company in the world, declared it was pouring up to $600 million over the next five to six years into the development of algae-based biofuels. At least $300 million is going to Exxon Mobil’s collaboration with Synthetic Genomics, a company founded by the molecular biologist Craig Venter. Synthetic Genomics plans to use genetically modified (GM) microalgae to produce a variety of biofuels and may even tweak some organisms to directly produce hydrocarbons, which can then be refined into gasoline, jet fuel, and other products. The oil giant’s task in this is to develop a refining and distribution infrastructure that can lift the production of algal biofuels to high-volume, commercially sustainable levels.

The Exxon Mobil announcement appears to be the largest single investment yet in the burgeoning algal biofuels industry, but further major deals seem imminent. The US government committed nearly $800 million in funding for advanced biofuels research in May, and numerous other companies are also planning to produce fuel from algae and are seeking funds from investors. In June, two algal biofuel companies, Solix Biofuels and Solazyme, each closed multi-million dollar investment deals. Later that month, Algenol Biofuels announced a partnership with Dow Chemical to create a demonstration plant in Texas capable of creating 100,000 gallons of ethanol a year from GM algae. In July, Joule Biotechnologies unveiled plans for a process it claims could create 20,000 gallons of biofuel from a single acre over the course of a year, using colonies of small GM photosynthetic organisms. (The company refuses to disclose which organisms will actually be used.)

Each of these companies has its own take on algal biofuels. Even tiny tweaks in process and feedstock can dramatically change the efficiency of biofuel production, potentially making or breaking multimillion-dollar deals. Some companies rely on open ponds of algae; others use algae-filled enclosed photobioreactors. Several plan to use waste heat and carbon dioxide from power plants and other sources.

One of the key differences lies in how each company plans to extract biofuel from algae. Several species of algae naturally produce large quantities of oil, but this must then be extracted using energy- and time-intensive processes that typically kill the cells and thus reduce efficiency. Synthetic Genomics has developed GM algae that release oil naturally; Joule Biotechnologies and Algenol have both created GM organisms that secrete ethanol. These substances float to the top of the growth medium where they can be harvested, and GM cells, unharmed, continue their production. One company, OriginOil, has even developed a nonlethal harvesting technique using electrical impulses, perhaps targeted at ventures that haven’t created their own GM extraction methods.

Still, even with this flurry of research and investment in using algae to replace fossil fuels, they are only a small part of what needs to happen to combat climate change. Though technically carbon neutral—the algae recycle carbon dioxide that would otherwise be released into the atmosphere—that carbon dioxide will still find its way into the air when the fuel is burned. Perhaps further genetic tinkering could create algae tweaked not to produce biofuel, but to simply suck carbon from the atmosphere and convert it into forms not readily used by most living things. This, too, would be only a temporary fix and would likely be very difficult to achieve, but the accelerating pace of biotechnological intervention that has already enabled algal biofuels could render such wildly ambitious climate-change solutions feasible in the near future.